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18t Sprockets - advice needed.

11K views 82 replies 34 participants last post by  DaveM 
#1 ·
Hi Guys,
I've been busy this winter trying to get my own sevicing done. So far I've managed to change the oil and filter, spark plugs, fuel filter, changed to a K&N air filter. I've stripped and cleaned the front and rear brakes (what a difference having all the pistons moving - great improvement), unsiezed my chain adjuster, and am nearly ready to look at the suspension.
I've read a lot of posts referring to the use of the 18t front sprocket and would like to ask a couple of questions before I jump in the deep end.
Firstly what diference does it make to the power take up. I ride a lot in all weathers and would be concerned that fine throttle control in wet or icy/greasy/diesel covered roads may be more difficult.
Secondly are there any issues with the chain length. I will be doing the change at home using my centre stand and home tool kit, and wouldn't fancy having to chop out a link or two.
Thirdly does it affect chain life due to the extra force exerted by the smaller circumference pulley.
I'm really keen to do this, but just need some reassurance.

Regards and thanks,
Martin.

PS Can the Forum member I had the pleasure of meeting at the PSNI Trek at La Mon hotel get in touch. Due to too much Guinness I forgot your name.
 
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#2 ·
Everything will be fine. It doesn't turn it into a dragbike, just makes it better for sporty riding. The stock length chain works fine with mine. There's still plenty of adjustment left. I can't imagine it affects chain life significantly (if at all).
 
#6 ·
Hi Loosehead IMHO it is a great and simple cheap mod.

Unless maybe you do a lot of high speed Autobahn type riding the 18 tooth sprocket is the way to go.

I got 50,000kms out of my chain with the 18 th sprocket on and that was mostly 2 up mountain riding.

It makes take off from standstill and low speed manoeuvring easier and gives better drive out of corners in any gear.

It should make almost no fuel consumption difference either.

many here believe it should be std equipment but suspect noise control laws have caused the higher toothed 19 cog to be used instead.

There have been very few members who have regretted this mod and changed back.

DaveM:cool:
 
#7 ·
I am 1 who has changed back, as I do more long distance rides for touring & rallies etc
So the added speed/mpg/tank range the stock 19T gives suits me. the 18T makes me want to be a hooligan .........wheelying all the time ;)
 
#8 ·
There are no variations in calibration for any year RS or pre-'05 ST.

There is no down side that I am aware of. There is a massive improvement coming from full stop. The trade off is a few hundred RPM at cruising speed, barely worth mentioning.

Throttle response is better at very low speeds, though not so much better that you'll stay upright on ice. :p Seriously, the first time I went down on my RS was a rainy night coming off a stop sign on seriously beat-up pavement that had just had a coat of white paint in the crosswalk. I think I would have maintained control with the 18 where I lost it with the 19.

I suppose, in theory, it would be a good idea to run a chain that's one link shorter. In practice, there's no need.

Cheers, HTH,
-Kit
 
#9 ·
Thanks Guys,
Your prompt replies were much appreciated.Just the sort of soothing, positive replies I was after. Thanks for that link, Jim. I dont understand it all, but I can see that its not as drastic as I thought.
Sometimes I find I need a bit of reassurance that what I'm about to do is not as scary as I make it out to be.
It was only from reading all the stuff on this board that gave me the confidence to try out the routine servicing. Once I got started I had loads of fun, freezing cold hands, skinned knuckles, oil all over my garage floor. I also have clean oil, brakes that have never been this good and plans for doing loads more.
Regards,
Martin
 
#10 ·
Basically if you run the math there is a 500 rpm change. With these engines it's not worth thinking about.

Stock gearing is rather on the tall side and as DaveM said it's for noise drive by cert.

With the 18, around town is much easier and better for 2up.

No worries at all cruising and touring at 70 US mph = 4,000 rpm which is in the lower part of the torque curve anyway. These are not Massey Ferguson tractor motors and keeping them toward the middle of the torque curve is much better on them longevity wise and every thing else than lugging them around.

Mileage? I average 51 US mpg caning her butt off, what do you want egg in your beer? Actually, mine is much happier in an aggressive mode and gets better MPG than loafing on the interstate where it gets 47mpg.

Top speed? Trying both the 19 and 18 guess what? same top end at cut off in top gear with either sprocket. The 18 gets it there quicker though, much quicker. Better leverage (I slipped that one in again OnD:D)

I think I was the first to do this and my bike has been this way since about day one and would never consider going back to a 19.

There are no negatives to report on this modification.

A cheaper way to do it is to find an 18 off a TBird. TBird riders around here like the 19's and will swap. You local dealer might have a few stashed away but the AM ones aren't bad in price either.

Just do it you won't regret it.
 
#12 ·
I have just put on a JT myself. It was over $20 US. About $2 over, IIRC. ;)

Cheers,
-Kit
 
#16 ·
Two reasons, you'd probably need a longer chain and the difference would be minimal. You make gross rpm adjustments with the front sprocket and very fine tune with the rear.

Plus, changing out the front is easypeasy and the rear much more involved.

RSRAT has a good combo in the 18/45 but if one were thinking about that I'd wait for a chain change as you'd probably need a longer one and really, the 18/43 is very fine.

Don
 
#15 ·
I'm currently running an 18/45 combo on my RS and like it. Puts me at 5000rpm at 75mph- in the sweet spot- gets to 90 pdq when needed. Really helps in low and mid range twisties--because you can keep the revs and therefor intake suction up where you want it for better drive thru and out of turns. I think I'm seeing a little less driveline lash as well. no significant gas mileage change. Instead of going back to a 19 for any long trips, I think I'll be happy with just using a 44 or 43 on the rear- saves a good bit of work that way.

I used a JT at first for around 20 bucks but when I changed out my chain and rear sprockets I sprung for the oem 18t just because it is reputed to be a little smoother and quieter than the non rubber bushing JT. I can now sneak up on unsuspecting small animals.
 
#18 ·
I went 18/43 and the -1/+1 combo keeps the wheel within 0.5mm of stock wheelbase.
It's also making me lazy, top gear overtakes are an absolute doddle as long as I start well back and just keep it rolling. Well into 3 figure speeds after passing two artics from about a 50mph run up
 
#20 ·
I found it made it easier to keep the engine spinning while keeping to UK speed limits - with 19T, @30mph I always felt like I was in too high or too low gear. The 18T makes toddling round @30mph easier

Similarly for 70~75mph on dual carriageways.
Not the most glamorous selling point but handy now there seems to be speed cameras everywhere...
 
#21 ·
Geeze, you guys sound like DaveM did. Just have it done. It's the best/biggest bang for the buck performance wise you can do. And cheap too. Racing since the mid 60's this is about the only mod I've run across where there are no compromises. Meaning no negatives. It's what the bike was meant to have.
 
#24 ·
No engine adjustments at all needed. I think your speedo will be off though. 2004's and earlier take the speed off the front wheel so the sprocket change doesn't affect that.

Just pace someone and note the difference and the ratio will be the same throughout the speed range. These speedo's arent that accurate anyway, mine is about 10% optimistic. Most run 5-10% off.

No one has done it lately but there are some nifty small bicycle speedos that have been put on the bikes with the sensor taken off the front wheel. Or there is GPS too if it bothers one.
 
#25 ·
321Go: You can also use TuneBoy to correct the speedometer. I too have an '08 with an 18T countershaft sprocket. Tuneboy "110% trim factor" made the speedo nuts-on (according to GPS). Dang bike still won't pull the front wheel under power though... :sad: :policecar: :motorbike2:

CHEERS
 
#27 ·
Hmmm, it's one of the more subtle countershaft changes I've made, mainly because most bikes I've done this to started out with a 16T, 15T, or 14T so gearing down a tooth was mechanically more advantageous on those bikes. On the Sprinty, it actually took a few rides to notice. Acceleration feels slightly better, although not all that much. Around town, two-up, and from a dead stop, it really is easier to ride. Highway riding is just OK, but at 80mph it's spinning 5000rpm, which seems (to me) a bit busy for highway cruising. But the Trumpy never complains. There's no substitute for horsepower, and even with the 18T front sprocket, the bike is still underpowered IMO. For example, I feel a need to drop 2-3 gears to really blow by someone. I'm actually contemplating going down another tooth to 17. A proper motorcycle should pull the front wheel in 1st gear with the throttle. But that's just me, I'm a little (OK a lot) wierd about these things. My recommendation would be to go with the 18T unless you do mostly highway cruising at speeds at or above 80mph.
 
#28 ·
5k on these engines isn't busy, it's just starting to get into the fat part of the torque curve where it should be. My bike has spent it's life (touring?) a bit faster than that and spinning quite higher through the Coastal and Cascade mountains. No issues what so ever.

17 is too steep and rubbing block problems start in. I don't do intentional wheelies, the frame really isn't gusseted properly for those but they have been a by-product and my '02 has never had a problem powering through 3rd. Don't know what's wrong with your bike?

With a 17 one will definitely see more sky than earth. That's getting way too short for street usability and with the torque down low like we have not necessary.
 
#31 ·
I put one on for about 1000km and took it off again. I could hardly notice the difference, but then I'm more a tourer than a racer. The Sprint has plenty of get up and go for me without making it "busier".

For a significant difference I'd go the 17 tooth, but as stated above, it could cause other wear problems in the long run.
 
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